noise while making a phone call: hardware or software?
mail at mmontour.net
Fri Jan 4 04:08:56 CET 2008
Michael Shiloh wrote:
> I've been searching for this item but all I can find is bug # 883, which
> says it's a hardware issue, interference making its way into the GSM
> audio path one way or another.
> Does anyone recall any software explanation for this?
I've started to play around with the mixer settings, and it seems that
they can be tuned to reduce both the GSM "buzz" and the echo heard on
the remote end of the phone call. I don't yet have a set of "working"
state files - the Neo's mixer is quite complicated, and I don't have
access to the proper test equipment (tone generators, spectrum
analyzers, etc). However, I've found that a good first start is to set
to 0 the mixer controls of all of the unused components. There are some
that are physically not connected (e.g. Amp Mono), and others that are
unused in certain ALSA profiles (e.g. "Mono Voice" in the gsmhandset
profile). I will eventually get around to creating a patch for this, but
if someone else wants to do it first I won't complain.
There is also a hardware side to this issue - if the hardware was really
good at isolating the audio path from the radio signal, then there
wouldn't be an interference problem in the first place. However I don't
think it's reasonable to expect perfection. I can hear a GSM buzz
similar to the Neo's when my friend calls me from a Motorola RAZR, and
in general GSM seems to be much more interference-prone than my current
p.s. I'm using http://wiki.openmoko.org/wiki/Neo1973_audio_subsystem and
its linked pages as my reference. Another TODO for somebody would be to
annotate the codec block diagram with the ALSA names of the
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